Mirror smooth surface epoxy, wet sand, epoxy, paint whatever your fancy 2 days work.
Down side, epoxy seals the best, but does not soak in to the pores as good, so if you get a scratch you may get water inflitration.
Paint works great smooth finish,use a epoxy/plastix enamel (plasticoat is the best) the stuff you can get high on, you must be 18 to buy,
spit coat first, 3 coats of paint including spit coat. At least 3 days work if you dont what rinkles in paint. seals good.
So So surface 4 or 5 coats of poly, with a spit coat first. Paint whatever your fancy. 2 days work, whith fast dry poly. Down side, not as smooth or hard or helps stiffin the board, but better sealing, and can breath just a bit.